Caused by attachments in temp folder. attachments are named the same thing except a number 1-100 is added to the file. once it reaches 100, the file cannot be named that anymore and produces an error. This is the registry entry which gives the location of the temp folder. Delete the items in the temp folder and then it will be able to create the file again.   HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook\Security   2007: HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Security...